As Helpdesk agent you can restrict attachments visibility in Jira issues.

To do this you need:

1. to enable Allow to set attachments visibility option in Helpdesk administration:
   
   
   Now it is possible to set visibility for every attachment. You can do it by pressing cog-button:
   
2. After pressing it you need to select groups who will be able to see this attachment in Helpdesk portal;
   

If an attachment is restricted it has lock-icon on it: